Pipes used in pipe lines, chemical plants, power generation plants, mines, steel mills, pulp and paper plants, water filtration, sewage treatment plants and the like often carry contaminants that become deposited on the inside of the pipe. These contaminants are generally known as scale, and can be extremely hard, such as coke, calcium, silica, sulfur, iron sulfides and types of ceramic scale. Build up of the scale can cause a variety of problems from reduced production to rupture of the pipe. It is therefore desirable to remove the scale from the pipe.
Various prior art methods have been used to clean the inside of pipes including using wire brushes, steel shot blasting, high pressure water blasting and chemical cleaning. These methods have drawbacks such as incomplete removal of coke, increased pipe erosion and sagging, fire hazards, environmental concerns, long shut down, high cost and decreased production run lengths.
In U.S. Pat. No. 5,150,493, there is disclosed a pig that may be used to clean a pipe. The pig has removable appendages or pins disposed circumferentially around and extending radially outward from the elastomeric body of the pipeline pig. The pins are adjustable to various heights. The pig is forced through the pipe using hydraulic pressure, and the pins scrape the scale from the pipe. This pig has been found to be very successful in overcoming the problems with prior art methods of cleaning pipes.
In co-pending application Ser. No. 07/828,234, a method of use of the pig is described in which the pig is driven backwards and forwards through the section of the pipe that is contaminated with scale. In the case of very hard deposits, each pass through the contaminated sections removes a thin layer of scale. The method described there is expanded upon in this disclosure.
The location of coated sections can be identified by first running the pig through the pipe. The hydraulic pressure is monitored using pen recorders. At each bend in the pipe, a sharp pressure increase will be recorded. The location of the bends can be determined from a drawing of the pipe installation. When the pig encounters scale, there will be a pressure increase that corresponds to the degree of resistance met by the pig resulting from the scale. Greater pressure means greater scale build up. By running the pig through the pipe, a profile of the scale may be created. The location of the scale can be correlated to the known location of the bends. The scale itself can be flushed out with the hydraulic propellant and analyzed. The pin height and hardness can then be selected for the particular scale encountered. The pig may be run backwards and forwards primarily through contaminated sections. After several passes, the pig can be removed from the pipe and the pins replaced or moved radially outward by placing washers between at least some of the pins and the pig body.